fieldmarks: An unmistakable huge shark, one of three large filter-feeding species, with a broad, flat head and truncated snout, immense transverse, virtually terminal mouth in front of eyes, minute, extremely numerous teeth, and unique filter screens on its internal gill slits, prominent ridges on sides of body with the lowermost one expanding into a prominent keel on each side of the caudal peduncle, a large first dorsal and small second dorsal and anal fin, lunate or semilunate caudal fin without a prominent subterminal notch, and a unique checkerboard pattern of light spots, horizontal and vertical stripes on a dark background.

Body cylindrical or moderately depressed, with prominent ridges on sides. Head very broad and flattened, without lateral flaps of skin, snout truncated. Eyes laterally situated on head, without subocular pockets. Spiracles much smaller than eyes, behind but not below them.
Gill slits very large, fifth well separated from fourth. Internal gill slits with unique filter screens, consisting of transverse lamellae that cross each gill slit, with ramose processes on their inner surfaces that interconnect to form the filters.
Nostrils with rudimentary barbels and no circumnarial folds and grooves. Mouth extremely large, terminal on head, and transverse, without a symphyseal groove on chin.
Teeth not strongly differentiated in jaws, with a medial cusp, no cusplets and no labial root lobes; tooth rows extremely numerous, in over 300 rows in either jaw of adults and subadults.
Caudal peduncle with strong lateral keels and an upper precaudal pit.
Pectoral fins very large, relatively narrow and falcate, much larger than pelvic fins, with fin radials expanded into fin web nearly to its distal edge. Pelvic fins somewhat smaller than first dorsal but slightly larger than second dorsal and anal fins. First dorsal much larger than second, first dorsal with origin well anterior to the pelvic origins, and insertion over the pelvic bases. Anal fin about as large as second dorsal, with its origin about opposite first third of second dorsal base; anal fin with broad base and angular apex, separated by a space somewhat greater than base length from lower caudal origin. Caudal fin with its upper lobe at a high angle above the body axis, less than a third as long as the entire shark, with a vestigial terminal lobe and subterminal notch and a very strong ventral lobe or a very short one. Supraorbital crests present on cranium, these laterally expanded.
Valvular intestine probably of ring type.
A unique colour pattern of light spots and vertical and horizontal stripes, in the form of a checkerboard.

An epipelagic oceanic and coastal,tropical and warm-temperatepelagic shark, often seen far offshore but coming close inshore and sometimes entering lagoons of coral atolls. It is generally seen or otherwise encountered close to or at the surface as single individuals or in schools or aggregations of up to hundreds of sharks.In the Indian Ocean it is common around the Seychelles, Mauritius, Zanzibar, Madagascar, Mozambique and northernmost Natal. In the Western Pacific it is common in the Kuroshio current in the fishing grounds for skipjack. It is reportedly abundant from Cabo San Lucas to Acapulco in the Eastern Pacific, and in the Gulf of Mexico and the Caribbean in the Western Atlantic.It apparently prefers areas where the surface temperature is 21 to 25°C with cold water of 17°C or less upwelling into it, and salinity of 34-34.5 ppt; these conditions are probably optimal for production of plankton and small nektonic organisms, all of which are prey of the whale shark.
Whale sharks are apparently highly migratory, with their movements probably timed with blooms of planktonic organisms and changes in temperatures of water masses. They are often associated with schools of pelagic fish, especially scombrids.Development uncertain, possibly oviparous or ovoviviparous. In 1953 a large eggcase, 30 cm long, 14 cm wide and 9 cm thick containing a nearly full-term, 36 cm embryo whale shark was collected from the Gulf of Mexico, and the assumption was made that the species is oviparous (cf. Baughman, 1955, Garrick, 1964, Bass, d'Aubrey & Kistnasamy, 1975). However, the rarity of 'free-living' whale-shark eggs, the extreme thinness and lack of tendrils on the only known case, the considerable yolk and partially developed gill sieve in the only known embryo, and the presence of umbilical scars on larger free living specimens 55 cm long suggests an alternative explanation (Wolfson, 1983), that the Gulf of Mexico egg was aborted before term, and that the whale shark is ovoviviparous. The type of ovoviviparity practised by the whale shark would be a relatively simple sort very similar to that of the related nurse sharks (Ginglymostomatidae), with retention of the egg case in utero until the embryo hatches. Alternatively, the egg cases of the whale shark might be retained in utero for most of the development of their embryos, then ejected at a late stage of development. Hence the mode of reproduction of the whale shark must be considered uncertain, with ginglymostomatid-like ovoviviparity a distinct possibility. The smallest free-living whale sharks are 55-56 cm long, the smallest of which has an umbilical scar (properly vitelline scar). One adult female whale shark was recorded as having 16 egg cases in its uteri.
The whale shark is a versatile suction filter-feeder, and feeds on a wide variety of planktonic and nektonic organisms. Masses of small crustaceans are regularly reported, along with small and not so small fish such as sardines, anchovies, mackerel, and even small tunas and albacore as well as squid. The whale shark feeds at or close to the surface, and often assumes a vertical position with its mouth above. Phytoplankton often occurs in the stomachs of whale sharks, but whether this is a major component of the diet of this shark is rather doubtful. The suction-filter mechanism of the whale shark is more versatile than the dynamic filter mechanism of the basking shark in the range of prey species that can be taken. The basking shark, with its huge scooplike mouth, hydrodynamically 'clean' gill rakers, and huge gill slits, has little if any suction capacity and must depend on its relatively slow forward motion to carry animals into its mouth; this limits it to eating small planktonic crustacea and other invertebrates. [more...]

Size

Maximum total length uncertain, possibly to 18 m, but specimens rare above 12 m; 13.7 m is often given as the maximum measured, 12.1 m the most recently accurately measured. Most reported in the literature are between 4 to 12 m. Females of 438 to 562 cm are immature. This is by far the world's largest fish.

Interest to Fisheries

Apparently of relatively limited interest for fisheries. Small harpoon fisheries exist in Pakistan and India; it may also be taken in China, and has been captured and utilized in Senegal;it is eaten by people either fresh or dried salted and used to treat boat hulls in Pakistan.

Whale sharks have been fished sporadically in some tropical countries of the Indian and Western Pacific Oceans. In India, whale sharks were caught opportunistically for decades, but according to Hanfee (1998) a new targeted fishery developed recently in the coast of Gujarat mainly to supply export markets for whale shark meat (a trendy delicacy in Taiwan) and fins. Hanfee (1998) reports that according to Indian customs records, 200 t of whale shark meat were exported in 1995/96. According to Alava et al. (1998) whale shark fishing for meat, skins, and fins, has been a traditional activity for generations in the Bohol Sea that underwent a rapid expansion very recently. These authors estimated that a small-scale fishery with harpoons and gaff hooks took at least 624 whale sharks in four of the five primary fishing sites in the period 1990-96. The number of whale sharks caught per boat in two fishing sites decreased between 1993 and 1997 from 4.44 to 1.7 on one site and from 10 to 3.8 on the other (Alava et al. 1998). Whale sharks are a protected species in Philippines since 1998 when their killing was prohibited due to conservation concerns (Yaptinchai 1998). Whale sharks have been fished for several years off Taiwan (Province of China) but catches seem to vary erratically. Joung et al. (1996) report that catches used to be about 30-100 whale sharks per year but decreased to less than 10 by the late 1980s, whilst off a single fishing harbour more than 70 whale sharks were caught in 1992, only 2 in 1993 and 14 in 1994. In the Maldives, small-scale fishermen using gaff hooks (Anderson and Ahmed 1993) fished whale sharks only for their oil. Anderson and Ahmed (1993) report that probably more than 30 whale sharks were fished per year in The Maldives during the early 1980s, but this apparently decreased to less than 30 by the early 1990s. The whale shark is a protected species in The Maldives since 1993 (Anderson 1993).

Conservation Status : The IUCN Red List considers the whale shark a Data Deficient species worldwide (Camhi et al. 1998). However, the apparent decreasing catch rates in some of the fisheries outlined above suggest that whale sharks, like most elasmobranchs, are susceptible to overfishing when exploitation runs unchecked. Whale sharks are currently protected in several parts of the world: in Australia (Western Australia); The Maldives; The Philippines, and in the USA (Florida state Waters and all federal waters of the Gulf of México and Atlantic coast). Additional information from IUCN database Additional information from CITESdatabase

Remarks

There has been considerable variation in spelling of the generic name of the whale shark, and much usage of several of the variants. Although Rhiniodon has priority, the variants Rhincodon and Rhineodon (and to a lesser extent Rhinodon) have had much more usage. Following Bigelow & Schroeder (1948) the variant Rhincodonhas developed a considerable 'public', and proposals to stabilize it (Robins & Lea, 1975; Swift, 1977) have been presented to the International Commission on Zoological Nomenclature. In contrast Hubbs, Compagno & Follett (1976) proposed that the earliest spelling, Rhiniodon should be preserved for the whale shark because of priority, more correct orthography than Rhincodon, and because the use of Rhincodon has not been universal since Bigelow & Schroeder's work. At present the International Commission has yet to hand down a ruling on the matter and, until it does, I prefer to use the earliest spelling (Rhiniodon).Threat to humans: The whale shark is generally considered harmless, and very large individuals examined and ridden by divers without the sharks reacting aggressively, although they may show curiosity and approach divers to apparently examine them. However, there have been a few cases of whale sharks butting sportfishing boats, possibly after being excited by hooked fishes being played from the boats or by bait. More often human beings inadvertently assault whale sharks, by ramming them with ships and boats as they bask on the surface.